It is known in the art that photographic display materials are utilized for advertising, as well as decorative displays of photographic images. Since these display materials are used in advertising, the image quality of the display material is critical in expressing the quality message of the product or service being advertised. Further, a photographic display image needs to be high impact, as it attempts to draw consumer attention to the display material and the desired message being conveyed. Typical applications for display material include product and service advertising in public places such as airports, buses and sports stadiums, movie posters, and fine art photography. The desired attributes of a quality, high impact photographic display material are a slight blue density minimum, durability, sharpness, and flatness. Cost is also important, as display materials tend to be expensive compared with alternative display material technology, mainly lithographic images on paper. For display materials, traditional color paper is undesirable, as it suffers from a lack of durability for the handling, photoprocessing, and display of large format images.
In the formation of color paper it is known that the base paper has applied thereto a layer of polymer, typically polyethylene. This layer serves to provide waterproofing to the paper, as well as providing a smooth surface on which the photosensitive layers are formed. The formation of a suitably smooth surface is difficult requiring great care and expense to ensure proper laydown and cooling of the polyethylene layers. The formation of a suitably smooth surface would also improve image quality, as the display material would have more apparent blackness as the reflective properties of the improved base are more specular than the prior materials. As the whites are whiter and the blacks are blacker, there is more range in between and, therefore, contrast is enhanced. It would be desirable if a more reliable and improved surface could be formed at less expense.
Prior art photographic reflective papers comprise a melt extruded polyethylene layer which also serves as a carrier layer for optical brightener and other whitener materials, as well as tint materials. It would be desirable if the optical brightener, whitener materials, and tints, rather than being dispersed a single melt extruded layer of polyethylene, could be concentrated nearer the surface where they would be more effective optically.
Prior art photographic transmission display materials with incorporated diffusers have light sensitive silver halide emulsions coated directly onto a gelatin coated clear polyester sheet. Incorporated diffusers are necessary to diffuse the light source used to backlight transmission display materials. Without a diffuser, the light source would reduce the quality of the image. Typically, white pigments are coated in the bottommost layer of the imaging layers. Since light sensitive silver halide emulsions tend to be yellow because of the gelatin used as a binder for photographic emulsions, minimum density areas of a developed image will tend to appear yellow. A yellow white reduces the commercial value of a transmission display material because the imaging viewing public associates image quality with a white white. It would be desirable if a transmission display material with an incorporated diffuser could have a more blue white, as this is perceived by the public as the whitest white.
Prior art transmission display materials use a high coverage of light sensitive silver halide emulsion to increase the density of the image compared to photographic reflective print materials. While increasing the coverage does increase the density of the image in transmission space, the time to image development is also increased as the coverage increases. Typically, a high density transmission display material has a developer time of 110 seconds compared to a developer time of 45 seconds or less for photographic print materials. Prior art high density transmission display materials, when processed, reduce the productivity of the development lab. Further, coating a high coverage of emulsion requires additional drying of the emulsion in manufacturing reducing the productivity of emulsion coating machines. It would be desirable if a transmission display material was high in density and had a developer time less than 50 seconds.
Prior art photographic transmission display materials with incorporated diffusers have light sensitive silver halide emulsions coated directly onto a gelatin subbed clear polyester sheet. TiO.sub.2 is added to the bottommost layer of the imaging layers to diffuse light so well that individual elements of the illuminating bulbs utilized are not visible to the observer of the displayed image. However, coating TiO.sub.2 in the imaging layer causes manufacturing problems such as increased coating coverage which requires more coating machine drying and a reduction in coating machine productivity as the TiO.sub.2 requires additional cleaning of the coating machine. Further, as higher amounts of TiO.sub.2 are used to diffuse high intensity backlighting systems, the TiO.sub.2 coated in the bottommost imaging layer causes unacceptable light scattering reducing the quality of the transmission image. It would be desirable to eliminate the TiO.sub.2 from the image layers while providing the necessary transmission properties and image quality properties.
Prior art photographic display materials use polyester as a base for the support. Typically the polyester support is from 150 to 250 .mu.m thick to provide the required stiffness. A thinner base material would be lower in cost and allow for roll handling efficiency, as the rolls would weigh less and be smaller in diameter. It would be desirable to use a base material that had the required stiffness but was thinner to reduce cost and improve roll handling efficiency.
An example of coextruded thin layer technology improvements and limitations is explained in U.S. Pat. No. 5,476,708 where it is proposed that sharpness improvements in photographic systems can be achieved by an untinted, unpigmented melt extruded thin skin made to be used under a light sensitive emulsion. It would be desirable if a thin skin under the emulsion could be both biaxially oriented to provide stiffness and tinted blue to provide the necessary color correction for the yellowness of the light sensitive silver halide imaging layer.